Science Questions

What is the smallest thing that is possible to see with a microscope?

Sun, 14th Feb 2010

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Pekka Keskinen asked:

What is the smallest thing that is possible to see with a microscope?


Dave -   It depends on the kind of microscope.  Light behaves a bit like a wave. It has a wavelength.  Itís very, very hard to see things smaller than the wavelength of the light because you essentially get interference effects. The waves interfere and it messes with your picture.  With conventional microscopes itís very hard to see anything less than the wavelength of light which is about half a micrometer - roughly a 2000th of a millimetre.  There are ways of doing things with light which means you can get a little bit smaller than that, using funky things called metamaterials, but they are not really common.

If you want to get much more magnification than that you need to use something with a much smaller wavelength.  A common one to use is an electron, because although it appears like a particle itís also a wave and the wavelength is much, much shorter and therefore you can see much, much smaller things.  You can actually see big atoms with a normal electron microscope.  Other forms of microscope involve dragging a tip, itís called a scanning tunneling electron microscope, and you measure the electric current going between your tip and your object  - with this, you can measure down to large atoms.

Chris -   IBM iconically produced the letters IBM, I think it was 1990-1991, by manoeuvring Xenon atoms with a scanning tunnelling electron miscroscope didnít they?  I canít remember quite many atoms they used, 40 or something, and it took them about 2 weeks to move these things around.  People were saying this is the future of computing! 

There was also a story that got published in the middle of 2008.  It was by a researcher at the University of California, Berkley, Jannik Meyer.  This was a wonderful paper because they were able to see hydrogen atoms.  That probably qualifies as the smallest thing you could see because thatís the smallest entity at an atomic level in the Universe. 

The way they did this was they had a sheet of graphene which is a single layer, one carbon atom thick, of graphite and they could drop molecules onto that surface and then scan across it with the scanning tunnelling electron microscope and measure where it was interacting.  The tip was interacting with the different atoms. 

Because the graphene is like a little pattern of chicken wire - itís a very regular hexagon pattern - itís very easy to subtract mathematically from whatever signature you pick up, so they can see any atomic species that were dropped on there.  They could even see these little white dots that turned out to be hydrogen atoms; if you put a bigger molecule, like a butane molecule - the stuff that you burn in your lighter - on there, you can actually see this zig-zagging chain of hydrocarbons. Itís just absolutely phenomenal!


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I think you can see smaller things that that by angling the stream of electrons you use to produce a effect on the object you observe? I read something about it but i don't remember where? It's more of an indirect observation due to what we already know of how 'matter' react to our microscope. Anyone that recognizes this? And we do have 'photos' of electrons(?) Well, their 'orbitals' at least. But the new thing in 'observing' is the idea of indirect observation where we due to known interactions can see if 'something' has changed some state, without us directly interfering with the object. This idea comes from the hope of us being able to 'go around' HUP (Heisenberg's uncertainty principle) and actually influence a particle without locking it into a certain 'state' by directly observing it, as well as getting knowledge of processes to small to observe directly by the waves we send from our microscope. What you want to see can't be smaller than the wavelength you use to look at it, so that puts a limit to what you can observe directly.

As I remember it :) yor_on, Tue, 16th Feb 2010

Don't one end up with a mini-black hole if try to increase the resolution (and frequency -hence energy) of the photon above a certain value?

If so, would it means that the smallest bits of nature are in fact not accessible to us since what is inside the mini-black hole is not in a causal relation with us?(by no causal relation I mean that we cannot see beyond event horizon).

flr, Wed, 17th Feb 2010

Yep, you're correct flr.

In principle, a black hole can have any mass above the Planck mass. To make a black hole, one must concentrate mass or energy sufficiently that the escape velocity from the region in which it is concentrated exceeds the speed of light.

This condition gives the Schwarzschild radius, R = 2GM / c2, where G is Newton's constant and c is the speed of light, as the size of a black hole of mass M. On the other hand, the Compton wavelength, λ = h / Mc, where h is Planck's constant, represents a limit on the minimum size of the region in which a mass M at rest can be localized.

For sufficiently small M, the reduced Compton wavelength (\lambda = \hbar/Mc , where ħ is Dirac's constant) exceeds half the Schwarzschild radius, and no black hole description exists. This smallest mass for a black hole is thus approximately the Planck mass.

Some extensions of present physics posit the existence of extra dimensions of space. In higher-dimensional spacetime, the strength of gravity increases more rapidly with decreasing distance than in three dimensions. With certain special configurations of the extra dimensions, this effect can lower the Planck scale to the TeV range.

Examples of such extensions include large extra dimensions, special cases of the Randall-Sundrum model, and String theory configurations like the GKP solutions. In such scenarios, black hole production could possibly be an important and observable effect at the LHC. It would also be a common natural phenomenon induced by the cosmic rays.

---End of quote---


Let's apply the logic on a Rindler observer.
At what uniform velocity will the Rindler observer see virtual particles transform into 'Black Holes'?
And, can they? yor_on, Wed, 17th Feb 2010

I think I found it, at last :)

"in 1928 E.H. Synge suggested that one could beat this limit by ísqueezingí light through a subwavelength-size hole in an opaque screen. The light will spread quickly due to diffraction once it emerges from the other side of the hole, but if the hole is brought very near to an object to be Ďimagedí, one can illuminate that object with a light spot whose size is no larger than the hole in the screen. Light is focused by a lens from below onto a collection of brown particles. With the lens alone, one cannot shine light on individual particles: at best, one will always illuminate three of them. If an aperture of width 1/3 of the wavelength is used to block the light, we can illuminate a single particle at a time. However, those particles must be close to the aperture, because the light field spreads rapidly upon exiting it." yor_on, Mon, 1st Mar 2010

This technique is used in drum scanners where a bright image of the work being scanned is focused onto a aperture plate whence it passes thru a small hole onto the photo multiplier tubes.
An early form of TV transmitter tube (the Farnsworth image dissector) also used this principle syhprum, Tue, 2nd Mar 2010

In principle, you can see, with the unaided eye, a single atom. You just need to illuminate it brightly enough that it reflects or fluoresces enough light in the direction of your eye to see and you also need to do this against a dark background.

As far as I know nobody has quite done this yet, but they have done spectroscopy on single (fairly small) molecules. Bored chemist, Wed, 3rd Mar 2010

Optical Microscope, limit is around 30-40 thousand times.  Conventional microscopes hit a max around 1800 times.  Royal Raymond built a microscope that reportedly magnified 60,000 times.  Gaston Neassens built one around 30-40 thousand times.  Current commercially available microscope that is available can resolve down to 50 nm with white light. 

Note this is achieved using the grayfield method, provides variable depth of field at high magnifications, with true color, no parallax errors.

Please don't link to commercial websites - Mod Raid3, Tue, 25th Mar 2014

Has the mind got limits on scale in imagination? I just tried it, but, unsure how small the image was! Due to the subjective universe being created by the objective universe and imagination being dependent on objective 'seen' objects. ( like the fantasy 'uni corn' being a composite of a 'real' horn and a horse) would the minds of micro biologists, who have knowledge of objects at this scale, be more capable imagining micro objects or beings? I have been thinking about scale for awhile and I'm convinced that relative scale effects time. for example, if we were massive compared to the universe would the big bang be perceived to be like a instant flash, like a firework? but, as the universe is massive relative to us, time is slower and we perceive it to still be happening... sorry, pants at wording thoughts!! I personally feel one draw back to being human is we get locked in to thinking in terms of human scale. Peter J Steadman. (let me dream a life time and i'll be happy), Tue, 1st Apr 2014

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